Box Woods vs. Daylillies

I planted daylilies under a Red Bud and a Dog Wood in my garden several years ago when the trees were quite young. The trees have since grown to enormous height (I like to think it's all that stinky organic mulch I've been pouring in my garden all these years) and the daylilies are not flourishing in the trees' shade. I've trimmed the trees as much as I'm willing to, but it's still too shady. Is replacing the daylilies with a hedge of boxwoods (to later trim with annuals next spring) a viable idea? If so, is fall a good time to do it?